Anchor Shear Reinforcement Design Questions

[PSUEng11]

Good morning all,

I am working on a connection of a steel column to a concrete pier with shear transfer via the anchor bolts. Hopefully someone can help shed some light on this for me. I was looking over the Design of Anchor Reinforcement in Concrete Pedestals by Widianto, Patel, and Owen. I have seen this paper passed around a few times in various threads here, so I know that some are familiar with it. I do not think that I have seen these questions come up before in the threads, but please bear with me if they have.

In their recommendations, they state that the hooks of the enclosed stirrups have to be limited to a capacity of 0.9*fc'*eh*dtie (per ACI318-11 Eq. D-15 for hooked anchors) or a capacity of Atie*fs. They are assuming an Fs of 20ksi, based on recommendations by Ghali and Youakim, who cited testing done by Leonhardt and Walther. This appears to be based on older lower yield strengths of rebar compared to the typical 60ksi used today. The testing appears to be based on crushing of the concrete at the inner radius of the hook. The Ghali and Youakim paper notes that typically codes require heavier transverse bars at the hook to prevent this (i.e. vertical bar in a pedestal in a case that I am considering), but does not say anything about the capacity in the case where a heavier bar is present. The Widianto, Patel, and Owen paper notes that they assume that you have to consider the concrete as crushing, neglecting the presence of the heavier due to construction tolerances. It seems that they are also basing their assumptions on a smooth reinforcing bar vs. typical deformed bars.

I later also found a document/spreadsheet example on civil bay for anchor shear reinforcement design that appeared to be using the methods discussed in the paper and/or similar strut and tie method to design the ties. Their example did not check for the capacity of Atie*fs. They used Atie*fy for the full capacity of the tie and 0.9*fc'*eh*dtie for the pullout capacity of the hooked tie.

I have not really found any better references on this.

Ultimately my questions are:
- Does anyone really neglect the heavier bars due to construction tolerances? The bars will be there and the ties will be tied directly to the heavier bars.
- What capacities can be considered if we don't neglect the heavier bar present at the hook? Would I still have to use Atie*Fs with Fs=0.4Fy=24ksi (for current 60 KSI steel). I would have to think that it would be the full yield strength of the tie, so long as it is developed per ACI's requirements (12.13 which references 7.1.3 for #5 bars or smaller, calling for a standard stirrup hook), or 0.9*fc'*eh*dtie (per ACI318-11 Eq. D-15 for hooked anchors). [Then multiplying the limiting capacity by 0.75 per ACI D6.2.9].
- If we do neglect the heavier bars, what kind of capacities can be used based on deformed bars vs the referenced material's smooth bar testing?
- Does anyone have any other references that tries to clarify this?

Thanks for your help and input

 

[klaus.]

Why not add shear key for transfer of shear forces ??

 

[bones206]

I think the ASCE guide “Anchorage for Petrochemical Facilities” incorporated the Widianto stuff and may have expanded upon it. I don’t have it handy right now though, so I’m not 100% on that.

 

[PSUEng11]

Bones,

Thank you for the reply. That is a very good reference. They seem to incorporate the Widianto findings without changing anything (other than adding a few more tension reinforcing details and discussions). They don't really help answer any of my other questions, but I still think it is a good resource, so I appreciate it.

I did look into the referenced paper by Ghali on headed anchors, where they discuss some of the bar hook requirements. They discuss the bearing/crushing of concrete at the inner radius of the hook, correlating it to 0.4σy, as σ approaches fy. This furthers my belief and understanding that the bearing would have to be based on Atie * Fs = Atie * 0.4*Fy = 24ksi rather than the 20 ksi reported in the Design of Anchor Reinforcement in Concrete Pedestals (which still discusses smooth rebar ties as opposed to deformed bars) and still ignores the heavier bar at the hook.

Thanks for your help and input